1. Field of the Invention
The present invention relates to the field of vibration mounts.
2. Prior Art
The preferred embodiments of the present invention are intended for support of a shaker and attached test objects used to vibration test said objects, as well as general vibration isolation of structures as may be facilitated by low spring rate gas mounts, including but not limited to vibration testing in an environmental chamber.
Vibration mounts of various designs and for various purposes are well known in the prior art. In vibration mounts in general, it is desired to support a load with a low spring rate support to decouple the vibration of the load from the object the vibration mount is supported on, or to decouple the vibration of the object the vibration mount is supported on from the load, or in some cases to simply decouple the two vibration sources. Either way, the low spring rate is particularly important to isolate low frequency vibration, as the amplitude of a vibration of a given g level is inversely proportional to the frequency of the vibration. Static pressure air mounts are available for this purpose, with the inherent severe limitations of high static displacements and positional instability associated with the low spring rates and variable loading of these mounts. Any mount that reaches a limit of its travel in use, creates noise and injects higher frequencies and irregular vibrations, all counter to the purpose of the vibration mount. A simple, individually self leveling mount is desirable for many gas mount requirements. These requirements are not limited to vibration test, as they also apply to other applications as well, such as, by way of example, to isolate structures from floor or table borne vibrations as required by optical test benches.
In the case of the support of a shaker, various types of rubber mounts are used. Such mounts are satisfactory when resting on a rigid surface. However, because of the variation in the weight of various objects being tested, the combined weight of a object being tested and the shaker can vary significantly. Consequently, prior art vibration mounts for shakers tend to be somewhat stiff so as to not bottom out, so to speak, when testing heavy objects at low frequencies.
In one specific application, the floor panel in environmental test chambers is in general not rigid. In particular, the floor panel may be supported only along its edges, or if additional supports are provided, such supports are generally so limited as to not provide a rigid floor in other areas of the environmental chamber floor. Consequently, when a shaker is used in an environmental chamber with prior art vibration mounts, such as four mounts in a square pattern, one or more of those mounts will support the shaker more rigidly than the others. This has an adverse affect on the performance of the shaker, in that the support of the shaker is effectively displaced toward the more rigidly supported vibration mounts, injecting unintentional transverse vibration and rotational vibration perpendicular to axis the axis of the shaker, in addition to the intended linear vibration of the item under test along the axis of the shaker.